1. Field of the Invention
The present invention pertains to a method of etching organic antireflection coatings (ARCs). Organic antireflection coatings, as indicated by their name, include carbon and hydrogen containing materials, which are typically polymeric. The antireflection coatings are part of an etch stack used to produce semiconductor devices, and they are pattern etched to submicron dimensions. The present method permits uniform etching of ARCs over a semiconductor wafer surface, while providing control over dimensional shifts in the critical dimension of the etched feature size during etching.
2. Brief Description of the Background Art
In the field of semiconductor device fabrication, it is well recognized that as device feature sizes decrease to about 0.18 xcexcm and smaller, mask patterning via photoresist materials requires the use of deep ultra violet wavelength (DUV) imaging radiation. Antireflective coatings are used in combination with DUV photoresists, among other photoresists, to reduce standing waves and back scattered light, so that the dimensions of the patterning in the photoresist can be better controlled.
Generally the photoresist is applied over a stack of other layers which are patterned as a part of the semiconductor device fabrication process. Some of the layers in the stack are consumed during the process of patterning underlying layers which become part of the functioning device. An ARC layer may be present at a number of different locations within a stack of layers, depending on the application. When the ARC layer is applied over the top of a layer stack, it is referred to as a top antireflective coating (TAR), when the ARC layer lies beneath the photorcsist layer, it is commonly referred to as a bottom antireflective coating (BARC). TAR coatings are frequently removed during the photoresist patterning (developing) process, while BARC layers most often require dry etching removal.
Processes for the dry etching of organic ARCs usually are accomplished in a plasma etch system. ARC etching plasma source gases vary considerably in composition and may include, for example CHF3/CF4/Arxe2x80x94O2; CF4/Hexe2x80x94O2; O2/N2; HBr/O2; HBr/CO2/O2xe2x80x94Ar.
One process for etching organic antireflective coatings overlying a silicon-containing substrate is as follows. The substrate is placed into a process chamber and a process gas comprising oxygen and a compound selected from a group of compounds consisting of hydrogen and bromine-containing compounds, hydrogen and iodine-containing compounds, and mixtures thereof, is introduced into the chamber. A plasma of the process gas is generated in the process chamber to etch the coating. Processing variables are adjusted to provide anisotropic etching of the organic antireflective coating.
According to another etching process, an anti-reflection coating underlying a DUV photoresist is etched by employing a mixture of oxygen plasma, nitrogen plasma, and at least one inert gas. The antireflective coating layer can also be etched by employing a layer of nitrogen plasma and an inert gas, without the oxygen plasma, although the etch rate will be reduced.
Another method for plasma etching an organic buried antireflective coating (BARC) layer utilizes etch chemistry provided by a plasma processing gas which includes hydrogen bromide (HBr), CO2 and O2, with Argon or another inert material.
In general, the references pertaining to etching of organic layers and antireflective coating layers place great emphasis on maintenance of the critical dimension of the feature being etched, such as a line width, contact pad dimension, gate size, and so on. Emphasis is also placed on the selectivity of the etch process, where the etch rate of an ARC layer is compared with the etch rate of an adjacent layer of material, such as a silicon-containing layer underlying the ARC layer, for example. Another important variable, which is not as frequently addressed, is the etched feature critical dimension uniformity control across a substrate, such as a semiconductor wafer. For example, when the pattern being etched into an ARC layer is a series of lines and spaces, and the spacing between the lines is different at different positions on the substrate surface, the etch rate of the ARC may vary at different positions on the substrate surface. This may affect the depth of etch and may affect the profile of the feature being etched. It also affects the critical dimension uniformity across the substrate. The phenomenon of a change in overall etch performance across a substrate surface as a function of the spacing between etched features is sometimes referred to as a xe2x80x9cmicroloadingxe2x80x9d effect. Differences in etch rate and/or etched feature profile occur in part because the availability of etchant species at a given position on the substrate surface varies, and the amount of etch byproduct which is produced at a given position varies. One of the reasons the availability of etchant species and byproduct residue vary across a wafer surface is that the input and distribution of processing gases and the removal of processing gases and etch byproducts from the processing chamber is not always uniform. Another reason is that there is different spacing between pattern features at different locations (positions) on the substrate surface.
As the device size shrinks, there is less tolerance for nonuniformity of etch rate across the substrate surface and less tolerance for nonuniformity in the etched feature profile. The present invention discloses a method of etching organic layers, and in particular anti-reflective coating layers, which provides improved etch rate uniformity and improved critical dimension control of the etched feature across the substrate surface, while providing selectivity favoring etching of the antireflective coating layer relative to an underlying silicon-containing substrate.
The present invention relates to semiconductor processing, and to the plasma etching of organic layers, and in particular antireflective coating layers. We have discovered a particular combination of gases useful in producing chemically reactive plasma species, which provides unexpected control over etched feature critical dimension, etch profile, and uniformity of etch across a substrate surface despite a difference in the spacing of etched features over the substrate surface.
The combination of gases which produces chemically reactive plasma species consists essentially of CxHyFz/HBr/O2, where x ranges from 1 to 4, y ranges from 0 to 3, and z ranges from 1 to 10. Oxygen atoms may be substituted for about 30% of the hydrogen atoms in limited amounts in the CxHyFzformula. Essentially inert gases which do not produce chemically reactive species may be added to the CxHyFz/HBr/O2 combination of etchant-species producing gases. A combination of CF4/HBr/O2 has been demonstrated to work well.
Critical Dimension (CD) uniformity control across the surface of the substrate is generally improved by using a volumetric ratio of CxHyFz:HBr ranging from about 2:1 to about 5:1, with a range of about 3:1 to about 4:1 being preferred. A low pressure (less than about 20 mTorr), and a high plasma density (between about 1010exe2x88x92/cm3 and about 1011exe2x88x92/cm3) also helps improve CD uniformity control.
The volumetric ratio of (CxHyFz+HBr):O2 should range between about 1:1 to about 4.5:1, with a range of about 2:1 to 3:1 being preferred. An increase in the volumetric ratio up to at least about 3:1 tends to improve CD control at a given location on the substrate, while also improving the critical dimension uniformity across the wafer.